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Summary: The internally generated variability in the climate system, which is unrelated to any external factors, can be conceptualized as “noise”. This noise is a constitutive element of high-dimensional nonlinear models of such systems. In a three-layer nested simulation, which is forced by climatological (periodic) atmospheric forcing and includes an (almost) global model, a West-Pacific model, and South China Sea (SCS) model, we demonstrate that such “noise” builds also ocean models. They generate variability by themselves without an external forcing. The “noise” generation intensifies with higher resolution, which favors macroturbulence. Keywords: “Noise”, Internal variability, South China Sea, Eddies, Model resolution

This chapter covers our current understanding and recent advances in the study of Earth's ionosphere during magnetic storms and substorms with a special focus on electrodynamics and its consequences in the past 14 years. In particular, the focus is on the new awareness of looking at the magnetosphere, ionosphere, and thermosphere (M-I-T) as a whole system that has brought us to the next level of understanding. Both ground-based observations and the new space-based observations from magnetospheric missions are expanding rapidly. More and more compelling science questions cannot be addressed and resolved without combining simultaneous multiple observations in the ionosphere, plasmasphere, and magnetosphere in order to establish a consistent understanding of the system. Models have greatly improved mostly by coupling different regions and different species. New models can reproduce system phenomena that involve M-I-T coupling and help us elucidate the underlying processes within the coupled systems. Our future challenges will involve (1) cross-scale system and scale interactions; (2) the whole geospace modeling concept, including lower atmospheric forcing; (3) multiday forecasting capability.

A performance study of seven regional ocean configurations based on NEMO has been carried out for the Adriatic Sea over a common period (1980–2012). Assessed models differ in resolution, model physics, atmospheric forcing (forced vs. coupled models) and river discharges imposed within the Adriatic Sea. Models have been evaluated on the long-term temperature and salinity measurements in all of the Adriatic sub-basins, in particular within dense water collectors (Jabuka Pit and South Adriatic Pit) and dense water formation sites (northern and southern Adriatic). Adriatic-wide salinity content is mostly linked to the proper introduction of the overall water budget, rather than to the local river forcing. Forced models mostly overestimate temperature and salinity values. On average, coupled models better reproduce the thermohaline properties and processes, in particular the Adriatic-Ionian Bimodal Oscillating System (BiOS) reversals and its decadal variability. Wintertime heat losses are playing major role in defining the Adriatic Deep Water (ADW) transport rates in coupled models, while in forced models preconditioning in salinity is the most important factor. Further on, increase of resolution of the atmospheric forcing results in more realistic ocean behaviour, including dense water formation (DWF) in the complex coastal northern Adriatic. However, all models have large temperature biases and lower deep stratification at the dense water collector sites, indicating overall underrepresentation of the Adriatic DWF. Consequently, mixed-layer depth in the southern Adriatic is overestimated, reaching the bottom during some years. Ocean model resolution and river forcing seem to play a second-order role in defining the overall Adriatic-Ionian thermohaline properties, while inclusion of aerosol trend only slightly modified the BiOS reproduction., One simulation was performed using HPC resources from GENCI-[TGCC/CINES/IDRIS], Grant 0227). AVISO+ product were downloaded from https://www.aviso.altimetry.fr. This work is a part of the Med-CORDEX initiative (www.medcordex.eu) and a contribution to the MISTRALS/HyMeX programme. The support from Croatian Science Foundation is acknowledged through projects ADIOS [HRZZ grant IP-06-2016-1955] and SCOOL [HRZZ grant IP-2014-09-5747].

The DISASTER database records 1969 unique hydro-geomorphologic cases (floods and landslides) that generated human damages in Portugal during a 150 year-period (1865–2015. The main purposes of this work are the following: to present a national disaster events catalogue; to analyse the atmospheric conditions and to discuss the role of rainfall as main driving force of the hydro-geomorphological disaster events. The main Circulation Weather Types (CWTs) and the presence of Atmospheric Rivers (ARs) of each day of the disaster events were classified using the 20CR dataset (1865–2014) and the NCEP/NCAR reanalysis (2015). These datasets were used to compute the daily cumulative precipitation and the long term climatological year accumulated precipitation 10th, 50th, 90th and 95th percentile spanning 1865–2015 and the accumulated rainfall conditions after and before each disaster event. In the central and northern Portugal Disaster events are mainly driven by southwest (SW), west (W), northwest (NW) and Cyclonic (C) Weather Types, whereas the CWTs with a southern and eastern component [east (E), southeast (SE) and south (S)] are the main drivers in the south part of the country. Cyclonic CWT is widely associated with convective systems that can generate flash floods and urban floods often responsible for fatalities and injured people. CWTs with a westerly component can be associated to prolonged wet periods that can induce flood events in the main rivers and landslides in the mountain areas. The methodology used to build this disaster event catalogue can be applicable to other study areas, namely the North Atlantic and the Mediterranean regions, where the flood and landslides extremes are related to the atmospheric circulation.

The relationships of Mediterranean sea level, its atmospherically driven and thermosteric components with the large scale atmospheric modes over the North Atlantic and Europe are explored and quantified. The modes considered are the North Atlantic Oscillation (NAO), the East Atlantic pattern (EA), the Scandinavian pattern (SCAN) and the East Atlantic/Western Russian (EA/WR). The influence of each mode changes between winter and summer. During winter the NAO is the major mode impacting winter Mediterranean sea level (accounting for 83% of the variance) with SCAN being the second (56%) mode in importance. Both NAO and SCAN effects are partly due to direct atmospheric forcing of sea level through wind and pressure changes. However NAO and SCAN are correlated with each other during winter and they explain the same part of variability. The EA/WR also affects the atmospheric sea level component in winter (13%), acting through atmospheric pressure patterns. In winter, the thermosteric contribution is correlated with the SCAN in parts of the Eastern Mediterranean (9%). The rate of change of the thermosteric component in winter is correlated with the EA (24%). During the summer season, the sea level variance is much reduced and the impact of the large scale modes is in most parts of the Mediterranean Sea non-significant, This work has been carried out in the framework of the projects VANIMEDAT-2 (CTM2009-10163-C02-01, funded by the Spanish Marine Science and Technology Program and the E-Plan of the Spanish Government) and ESCENARIOS (funded by the Agencia Estatal de METeorología). A. Martínez-Asensio acknowledges an FPI grant associated with the VANIMEDAT-2 project, M. Marcos acknowledges a “Ramón y Cajal” contract funded by the Spanish Government and G. Jordà acknowledges a JAE-Doc contract funded by the Spanish Research Council (CSIC) and the European Science Foundation

Inter-annual variability of calculated barotropic (netflow) and simulated baroclinic (inflow and outflow) exchanges through the Strait of Gibraltar is analyzed and their response to the main modes of atmospheric variability is investigated. Time series of the outflow obtained by high resolution simulations and estimated from in-situ Acoustic Doppler Current Profiler (ADCP) current measurements are compared. The time coefficients (TC) of the leading empirical orthogonal function (EOF) modes that describe zonal atmospheric circulation in the vicinity of the Strait (1st and 3rd of Sea-Level Pressure (SLP) and 1st of the wind) show significant covariance with the inflow and outflow. Based on these analyses, a regression model between these SLP TCs and outflow of the Mediterranean Water was developed. This regression outflow time series was compared with estimates based on current meter observations and the predictability and reconstruction of past exchange variability based on atmospheric pressure fields are discussed. The simple regression model seems to reproduce the outflow evolution fairly reasonably, with the exception of the year 2008, which is apparently anomalous without available physical explanation yet.The exchange time series show a reduced inter-annual variability (less than 1%, 2.6% and 3.1% of total 2-day variability, for netflow, inflow and outflow, respectively). From a statistical point of view no clear long-term tendencies were revealed. Anomalously high baroclinic fluxes are reported for the years of 2000-2001 that are coincident with strong impact on the Alboran Sea ecosystem. The origin of the anomalous flow is associated with a strong negative anomaly (~ - 9 hPa) in atmospheric pressure fields settled north of Iberian Peninsula and extending over the central Atlantic, favoring an increased zonal circulation in winter 2000/2001. These low pressure fields forced intense and durable westerly winds in the Gulf of Cadiz-Alboran system. The signal of this anomaly is also seen in time coefficients of the most significant EOF modes.The predictability of the exchanges for future climate is discussed. © 2013 Elsevier B.V., This study had the support of the Portuguese Foundation for Science and Technology (Fundação para a Ciência e a Tecnologia, FCT) in the frame of the MedEX Project (MARIN-ERA/MAR/0002/2008) and PEst-OE/MAR/UI0199/2011. D. Boutov was funded by FCT with a research grant SFRH/BI/51367/2011. In-situ outflow estimations were obtained in the frame of the Spanish funded INGRES Project (CTM2010-21229-C02). ECMWF ERA-Interim data used in this study have been obtained from the ECMWF Data Server (http://www.ecmwf.int/).

International audience; Simulating the oceanic circulation in Eastern Boundary Upwelling Systems (EBUS) is a challenging issue due to the paucity of wind stress products of a sufficiently high spatial resolution to simulate the observed upwelling dynamics. In this study, we present the results of regional simulations of the Humboldt current system (Peru and Chile coasts) to assess the value of a statistical downscaling model of surface forcing. Twin experiments that differ only from the momentum flux forcing are carried out over the 1992-2000 period that encompasses the major 1997/98 El Niño/La Niña event. It is shown that the mean biases of the oceanic circulation can be drastically reduced simply substituting the mean wind field of NCEP reanalysis by a higher resolution mean product (QuikSCAT). The statistical downscaling model improves further the simulations allowing more realistic intraseasonal and interannual coastal undercurrent variability, which is notoriously strong off Central Peru and Central Chile. Despite some limitations, our results suggest that the statistical approach may be useful to regional oceanic studies of present and future climates.

The sensitivity of North Sea physics and phytoplankton production to atmospheric forcing has been studied by performing perturbations of the atmospheric forcing fields through a number of model simulations. The perturbations are kept in the range of expected climate change, to give a first indication of the climate change impacts on regional systems. The model simulations suggest that an increase in air temperature and short wave radiation will increase sea surface temperature, while an increase in wind will decrease it. Increased wind will increase the transports into the North Sea, while the other atmospheric forcings only have a small impact on that. Combining the perturbations indicates a smaller stratified area and a deeper mixed layer. Primary production is expected to increase, with an increase in wind speed having the largest impact.

12 pages, 13 figures, 1 table, The surface salinity response to changes of various external forcings and model parameters is investigated in a regional 1/3° configuration of the NEMO-OPA model implemented over the eastern North-Atlantic subtropical Ocean. Fourteen realistic climatological simulations are run. By default, neither relaxation to climatological surface salinity nor temperature is included. Forcing fields and parameters expected to impact the surface salinity are modified. These include: the wind stress, the surface temperature, wind speed and relative humidity entering the bulk calculation for sensible and latent heat fluxes, the precipitation, the data specified at open boundaries, the lateral viscosity operator, the salt lateral diffusivity, the vertical mixing scheme, the on/off switch of the double diffusion parameterization, the river runoffs and the SSS/SST restoring terms. The SSS standard deviation over this ensemble of model simulations is of the order of 0.1 psu, which is also the order of the annual cycle of the surface salinity field in this area., In this experimental framework, the wind stress is found to have the largest impact on the model SSS, both in terms of mean field and annual variability. The sensitivity to the precipitation, atmospheric temperature, open boundary external data, and to the relaxation to climatological SSS and SST, is also significant. Of all the model parameterizations, the lateral salt diffusivity is the one associated to the strongest surface salinity model response. This work allows the identification of the main sources of error for model surface salinity. It paves the way for a more comprehensive investigation of SSS model error statistics, which is needed for future data assimilation experiments motivated by the close launch of the new SSS-observing SMOS and Aquarius satellite missions, This work was supported by the Spanish National Program on Space, under contracts ESP2004-00671 and ESP2005-06823-C05

14 páginas, 12 figuras, 3 tablas, Upwelling events driving ENACW(Eastern North Atlantic CoastalWater) into the Galician western coast rias had been considered typical spring–summer processes, according to the research developed in this area. However, they can also be observed in fall or winter under northerly winds blowing at shelf. Six different upwelling events were analyzed in the Ria of Pontevedra during the wet season (NDJF) from2000 to 2005. These events were characterized bymeans of the zonal Ekman transport (Qx) at four control points in front of the western rias (locally known as Rias Baixas) and thermohaline variables measured at a fixed station in the main mouth of the Ria of Pontevedra. The duration of the upwelling events ranged from27 days (during February andMarch 2002) to 69 days (duringNovember– December 2004 and January 2005). Upwelling events studied in the Ria of Pontevedra from 2000 to 2005 showed the similarity in upwelling features during both seasons (similar wind forcing and upwelled water). Finally, Qx was correlated with the most representative atmospheric patterns in the Northern Hemisphere (EA, NAO, EA/WR, POL and SCA) from1966 to 2005. The winter EA pattern has the most influence on Qx showing an annual evolution with a prevalence of the positive phase from 1976 on. This positive phase is directly correlated with a prevalence of positive values of Qx which are upwelling unfavorable in the Rias Baixas., This work is a contribution to the Spanish LOICZ coordinate project METRIA supported by the CICYT under projects MAR96-1782, REN2003-04106-C03 and CTM2006-05882-C04-03/MAR and by ‘Xunta de Galicia’ under projects PGIDIT06PXIB383285PR and PGIDIT06PXIB383288PR.

The ocean around Iceland has much to offer in terms of interesting physical oceanographic phenomena. Among these phenomena are great contrasts in water mass properties, strong atmospheric forcing in the area, both dynamic and thermodynamic, and the fact that a large part of the thermohaline circulation of the world ocean has its origin there or passes over the ridges on either side of the country. Icelandic waters also show large interannual and decadal variability. In recent years, research has been more oriented towards quantitative studies. In this paper we will illustrate some of those properties using examples from recent research projects carried out in the area. Oceanographic research in the area around Iceland has a long history. In the 19th and the beginning of the 20th century, the research was mostly conducted by other nations. Now the oceanographic research is done mostly by Icelandic institutions, often in close co-operation with foreign colleagues.

The Mediterranean Forecasting System Pilot Project (1998-2001) has been completed and every week a ten days forecast is released on the Web ( http://www.cineca.it/mfspp ). This is realised with a networking of Near Real Time observing and modelling centres started within the project and working operationally from January 2000. The network consists of: 1) three data centres that provide in situ and satellite data for initialisation of model forecasts. The observations are released with a time delay of one to three days through the internet; 2) a meteorological data centre for the collection and transmission of atmospheric forcing fields; 3) a central modelling and data assimilation centre which executes the forecasts. The satellite data consist of sea level anomalies and sea surface temperatures (SST) while the in situ data are temperature profiles acquired on Voluntary Observing ship tracks at biweekly frequency. All these data are assimilated to produce an initial condition for the forecast that is coupled asynchronously to atmospheric forecast surface fields. Skill scores indicate that RMS forecast error is lower than RMS persistence error after the first day in all Mediterranean regions.

Publisher Summary The primary goal of World Ocean Circulation Experiment (WOCE) is to obtain an understanding of the large-scale circulation of the world ocean, its time variability, and its impact on climate. Description and understanding of the oceans at basin and global scales is addressed during the WOCE Analysis, Interpretation, Modeling and Synthesis (AIMS) phase. From global WOCE (including altimetry) and pre-WOCE data sets and through improved modeling capabilities, it is evident that the ocean has vigorous variability on all time and space scales. Increasing emphasis is put therefore on the changing ocean state and its relation to changing atmospheric forcing conditions at time scales of intraseasonal to decadal. To proceed toward understanding this variability, a requirement of the WOCE synthesis phase is to provide the best possible description of the time-evolving ocean state during the WOCE period. WOCE syntheses merges information from various WOCE data sets to enhance the understanding of the ocean circulation in a way that is more complete than can be done from one data set or model alone. Three associated and overlapping activities are central to synthesis activities—namely, (1) analysis, (2) model testing and improvements, and (3) ocean state estimation.

A numerical model which solves the advective-diffusive dispersion equation for suspended matter and includes the deposition and resuspension is presented. The model requires the simultaneous solution of the hydrodynamic equations under tidal dynamics and atmospheric forcing, using time steps of a few seconds. The model has been applied to the Odiel river (southwest Spain). The hydrodynamic module has been widely validated for neap and medium tides, whereas the dispersion was calibrated against the dissolved 226Ra dispersion pattern. This 226Ra is discharged to the Odiel river from a phosphate fertilizer factory. The model was able to reproduce the observed behaviour of the suspended matter in the estuary. The sedimentation rates have shown that a net, although slow, sedimentation is being produced. Sensitivity tests were inconclusive with respect to parameters describing settling and resuspension, as internal processes within the estuary are overridden by the high influx and efflux of particulate material from the sea. Comisión Interministerial de Ciencia y Tecnología (CICYT) PB89-0621

The climatology of wet and dry regimes in five different regions of the contiguous United States is examined using station records of daily precipitation for the period 1931–86. The regions were selected to be representative of different climatological synoptic regimes, and hence are associated with different large-scale atmospheric forcing patterns. The results show that the precipitation-producing processes operating during the wettest and driest years are substantially different, with wet years generally displaying large increases in the heavier precipitation categories compared to the dry years. These differences may be related to changes in the large-scale atmospheric circulation patterns associated with the development of persistent oceanic anomalies associated with variations in air-sea exchange processes over the Pacific Ocean and, depending on the particular region of the country, in the Atlantic Ocean as well. It is shown that sequences of wet and dry years are rather common throughout the country. The 1930s and 50s saw prolonged periods of severe, and in some instances, extreme drought conditions in many parts of the country. There does not appear to be any secular trend in the frequency of either wet or dry regimes through the analysis period. Wet conditions prevailed in much of the country in the early 1980s; a return to drier conditions in the past couple of years, therefore, appears to be just a normal swing to an opposite regime.

The generation of low-frequency current fluctuations in the ocean by variable winds is reconsidered. Observed spectral characteristics of the wind field over the ocean are discussed. A simplified analytical model is used to derive spectral properties of the oceanic response to broadband atmospheric forcing. The results qualitatively agree with a more realistic numerical model, and may help to explain some aspects of deep-sea current meter observations.

Publisher Summary This chapter discusses the residual circulation in the North Sea. Hydrodynamic models of the North Sea are primarily concerned with tides, storm surges, and the associated currents, which can have velocities as high as several meters per second. However, the period of the dominant tide is only about a half day and the characteristic lifetime of a synoptic weather pattern is of the order of a few days. The very strong currents that are produced by the tides and the atmospheric forcing are thus relatively transitory and a marine biologist argues that, over time scales of biological interest, they change and reverse so many times that they more or less cancel out, leaving only a small residual contribution to the net water circulation. The role of residual currents and residual structures in the dynamics of marine populations, the long-term transport of sediments or the ultimate disposal of pollutants is universally recognized. A detailed study of the tidal residuals in the North Sea was made by the means of two coupled three-dimensional models, one for tides and storm surges, and one for the residual circulation.

Results are presented from preliminary experiments with an ocean general circulation model of the equatorial Pacific Ocean. The model has been developed to be suitable for investigating the response of the equatorial Pacific Ocean to seasonal and interannual variations in atmospheric forcing. A comparison is made of the model responses during the first eighty days of integration forced by: (1) a purely zonal idealised wind-stress distribution; and (2) the annual-mean wind-stress field. This study shows the ability of the real wind field to excite equatorial waves from within the basin interior and the role of the horizontal advection in redistributing temperature. Significant differences between the frictionally dominated surface circulations in the two experiments are attributed to features of the real wind-stress distribution and in particular the existence of cross-equatorial components.

Observations in the Gulf of Guinea during the summer of 1974 provide new information about the onset of summer surface cooling in the eastern equatorial Atlantic. Dramatic variations observed in the hydrological structure of the upper layer during summer are described. The seasonal SST signal is interpreted in terms of an annual component superimposed on an almost permanent EI Nino-like phenomenon in the eastern equatorial Atlantic. This interpretation of the observations is supported by recent theoretical considerations which demonstrate the possibility of an eastern tropical Atlantic response to remote atmospheric forcing on a seasonal time scale. ..